Coating pigment and method of making same



Dec. 5, 1939. H, DE K 2,182,096

COATING PIGMENT AND METHOD OF MAKING SAME Filed June 15, 1957 CaCL No.1.CO3, (NaHCOQ REACTION TANK AND AGKTATOR CACQE,

CQCO5 ACCUMULPCHVE WEIGHT PERCENT PARTICLE DKAHETER. MIQQONS.

PULVERIZEK Ca C0 COATIN PIGMENT' IN VEN TOR.

f/owara/ Fad 6770i ATTOR 5Y5 mated Dec.5, 1939 I 2,182,096

UNITED STATES PATENT OFFICE COATING PIGMENT AND METHOD OF MAKING SAMEHoward Roderick, Grosse Isle, Mich., assignor to The Michigan AlkaliCompany, Wyandotte, Mich, a corporation of Michigan Application June 15,1937, Serial No. 148,347

4 Claims. (01. 134-58) The present invention relates to the manufacsizesof the calcium carbonate coating pigment ture of a calcium carbonatecoating pigment parembodying the principle of my invention. ticularlyadapted for use as a paper coating ma- The method of making my newcalcium carterial. The invention includes such a coating bonate coatingpigment involves the principal 5 pigment as a new article ofmanufacture, as well step of providing calcium carbonate by precipita- 5as the method of making it. tion from solution under certain prescribedcon- A coating pigment for use in the paper making ditions. The methoddescribed in my copendin art must possess a combination of the followingapplication Serial No. 98,202, filed Aug. 27, 1936, properties andqualities: good ink receptivity, serves as a basis for the practice ofthe present covering power, brightness, smoothness, and a process. Thismethod involves the precipitation 10 relatively low glue or adhesiverequirement. of calcium carbonate from the reaction between Heretofore,it has been found possible to make calcium chloride liquor anddecomposer liquor a calcium carbonate coating pigment in which Obtainedfrom the ammonia soda process. Such all of the properties except theglue requirement calcium chloride liquor contains approximately havebeen satisfactory, However, in such prior 100 t0 130 grams calciumchloride per liter and 15 art calcium carbonate coating pigments, theglue 60 $0 80 grams Sodium Chloride p e T or adhesive such as casein orother type of glue decompose! liquor i e by the Steam decom material,required to properly adh r d ,111 t position of a suspension of sodiumbicarbonate in pigment to the paper h b so great'as to watercontainsfrom 230 to 250 grams of sodium render such pigments economicallyprohibitive Carbonate p liter, and 50 to 100 grams Wide 20 i th papermaking industry Heretofore the composed sodium bicarbonate per liter.The calglue requirement of calcium carbonate coating cium chlorideliquor and h dBOOmPOSBI quo pigments has been in excess of an amount areintroduced e a tank and their sufflcient practically to prevent thecommercial temperature 15 memtemed 1n e range of e to 25 use f calciumcarbonate paper coating pigments 220: F. Such a reaction tank isprovided with a 25 previously known rap d agitator, and during suchreaction and agi- It is the general object n nature of my pres tation,calcium carbonate is precipitated from the ent invention to provide acalcium carbonate coatmlxed ing pigment having the property of arelatively The relative concentration of sodium carbonate low gluerequirement, in combination with the i l bicarbonate in the PP otherproperties and qualities of good ink recep is a very important factor indetermining the naf the resultant, precipitated calcium cartivity,covering power, brightness, and smoothtum 0 11885, so that the resultantproduct will be bonate product. It has been found that the best lts areobtained when the ratio of sodium mercially and economically acceptableto the paper making industry I have discovered that carbonate to sodiumbicarbonate in the decom- 35 1 1 a calcium carbonate coating pigment inwhich the fig hquor 1s m the range of from 2/2 to 3/2 particle size isgraduated in a range varying from Another factor which has an importantbear.. relatively coarse to relatively fine particle sizes ing upon theproduction of the desired product is possesses the combination of deemedproperties the presence of an excess of calcium chloride in and whereint e h requirement 15 as the reaction mixture at all times during themix- TO the P of the ferejgemg and ing process. Such excess of calciumchloride can related ends, said invention, then, consists of the bemaintained in the reacting solution by pumpea s hereinafter fullydescribed and Particularly ing the calcium chloride solution into thereaction Domted out 111 the claimstank at a much more rapid rate thanthe decom- 45 t e. annexed drawing e the followlng poser liquor; oralternatively, the calcium chloride sc p Set forth in detail 0116 methodand one liquor can be added to the reaction tank before productexemplifying my inventiePy Such the introduction of the decomposerliquor, and the closed procedure and product constituting, howprocessOperated as a batch 8:16 but 0!1e of Various pp o of the p The abovefactors of relative concentration of 50 males of my invention. sodiumcarbonate and sodium bicarbonate, and In said annexed drawing: thepresence of an excess of calcium chloride con- Fig. 1 is a flow sheetillustrating one method of tribute to the process the ability to producea making my new coating pigment; Fig. 2 is a diafine particle size ofprecipitated calcium carbogram illustrative of the desired range ofparticle nate. Conditions of temperature and rates of 55 agitation alsohave a bearing upon the resultant range of particle size of theprecipitated calcium carbonate.

Thus, for example, the greater the rate of agitation, the finer theparticle size; and the higher the temperature, the larger the particlesize. Therefore it can be said that the particle size of theprecipitated calcium carbonate from the reacting solutions varies ininverse proportion to the rate of agitation and in direct proportion tothe temperature, relative concentration of sodium carbonate to sodiumbicarbonate, and excess of calcium chloride. It has been found that atemperature of 150 F. with a relatively rapid rate 0 agitation is quitesatisfactory. I

Dependent upon the time in which the reacting solutions are in contactand present in the reaction and agitating tank, the subsequentdecomposition of calcium bicarbonate to calcium carbonate in a secondreaction or decomposing tank may be required. In this subsequentdecomposition, calcium bicarbonate is decomposed to calcium carbonatewith the evolution of carbon dioxide according to the followingequation:

Ca (HCOs) 2 CaCOa +H2O +CO2 Before pulverization Accumulative Diameterin microns percentage The above calcium carbonate is then subjected to apulverizing operation in a suitable manner, such as in either a pebblemill or a roll type mill,

'to a point where the particle sizes are distributed AccumulativeDiameter 111 microns percentage m s essaOOIOKQIOUOQ The glue requirementof the resultant product in which the particle sizes vary over a rangefrom relatively coarse to relatively fine sizes is as low as 7%.

Fig. 2 represents the data of Tables 1 and 2 in the form of plottedcurves, further illustrating the range of particle sizes and thepercentages theredefiocculate carbonate.

of in the final product. In Fig. 2, it will be seen that the particlediameter is plotted against the accumulative weight, and that thedifferent particle sizes after pulverization are relatively finer thanbefore pulverization; These two curves as 6 shown in Fig. 2substantially define the range of particle size distribution andlimits'prescribed for my new calcium carbonate coating pigment.

It will thus be seen that my invention provides calcium carbonatecoating pigment in which the particle sizes are varied or distributedover a range from relatively coarse to relatively fine, and that such apigment possesses the combination of properties and qualities of goodink receptivity, covering power, brightness, good finish or smoothness,and relatively low glue requirement, so that it is commercially andeconomically feasible for use in the paper making art.

The values in Tables 1 and 2 above were obtained by the settling method,being calculated by the use of Stokes law. This procedure, known inlaboratory parlance as the direct weight method, is herewith explainedin detail in order to enable those skilled in the art to comprehendfully the nature of the invention.

DIRECTIONS F012 OBTAINING PARTICLE SIZE BY SETTLING METHOD Materialsgrams carbonate sample.

5 g. casein. 5% NaOH soln. 12 10-in. test tubes. 12 5-in. test tubes. 12-liter beaker. 14 100-cc. beakers.

Procedure Soak carbonate in 1800 cc. distilled water for at least onehour, stirring-occaslonally. Mean- 40 while prepare the followingsolution. Soak five grams of casein in 100 cc. water for one-half hour.Then add sufl'icient alkali-to dissolve casein (about 1.6 cc. of 5%NaOH) and allow to soak for onehalf hour. Finally, heat 15 minutes at-140 F. and cool.

After carbonate has soaked for one hour, siphon 30 cc. into each ofseveral small test-tubes (agitation can be obtained by use of air jet).To each of these filled tubes add 0, 4, 8, 12, etc.,

- drops, respectively, of casein solution. This is done to determineamount of casein needed to Shake tubes and allow to stand one-half hour.The correct amount of casein solution to add is indicated by theformation of a precipitate that adheres to the bottom of the tube whenthe tube is gently tipped upsidedown. (Sometimes a bubble-like mass isnoted, but this is not the true indication.)

Add casein solution to the main body of car- 0 bonate solution in theproportion found to give defiocculation and agitate solution for onehour.

Graduate large test-tubes in following manner: put mark near bottom oftube at a definite volume (20 cc.) and another near top at a definiteheightv (19 cm.) from lower mark. I

Siphon deflocculated' solution into large, graduated tubes, filling tothe upper mark and noting time of filling. Draw oif solution from tubeNo. 1 down to lower mark five minutes after filling. Do same with No. 2at ten minutes and so on with the entire twelve tubes. Suggested timeintervals are 5, 10, 15, 25, 40, 60, 100, 150, 240, 480, 720, 1080 min.

. In addition, draw off a 50 cc. sample at the 75 r=particle rad. (cm.).

n=viscosity of solo. (poises).

h=height between marks (19 cm. in this case). A=sp. gr. of solid. d=sp.gr. of water (solvent).

9:980 cm. per sec.

t=seconds elapsed.

Substituting the values of aand h in the above equation and changing rto the diameter D, the following equation is obtained:

11 (Ad)t Upon changing D to microns, t to minutes, and n to centipoises,this equation of Stokes law reduces to the following form for use inthis method, viz.:

Other modes of applying the principle of my invention may be employedinstead of the one explained, change being made as regards the productandv method herein disclosed, provided the step or steps stated by anyof the followin claims or the equivalent of such stated step or steps beemployed.

I therefore particularly point out and distinctly claim as my invention:

1. A coating pigment for paper and the like consisting of calciumcarbonate of which 96%% has a particle size larger than 3 microns, ofwhich 91 has a particle size larger than 4 microns, of which 66% has aparticle size larger than 6 microns, of which 37%% has a particle sizelarger than 8 microns, of which 26% has a particle size larger than 10microns, of which 15%% has a particle size larger than 12 microns, ofwhich 12% has a particle size larger than 14 microns,

of which 9% has a particle size larger than 16 microns, of which 7% hasa particle size larger than 18 microns, of which has a particle 2. Acoating pigment for paper and the like consisting of calciumcarbonate ofwhich 82 has a particle size larger than 3 microns, of which 66 has aparticle size larger than 4 microns, of which 35% has a particle sizelarger than 6 microns, of which 19% has a particle size larger than 8microns, of which 12 has a particle size larger than microns, ofwhich.8% has a particle size larger than 12 microns, of which 5%%has aparticle size larger than 14 microns, of which 3 /2% has a particle sizelarger than 16 microns, of which 2 /g% has a particle size larger than18 microns, of which 2% has a particle size larger than 20 microns,ofwhich 134% has a particle size larger than 24 microns.

3. A method of making a calcium carbonate coating pigment for paper andthe like consisting in the steps of precipitating calcium carbonate fromreacting solutions of sodiumcarbonate, sodium bicarbonate, and calciumchloride, in which the relative concentration of sodium carbonate tosodium bicarbonate is in the range of 2 4 5 to 1, in the presence of anexcess of calcium chloride, agitating and heating such reactingsolutions during precipitation in a temperature range of 150 to 220 F.,filtering, washing, drying the precipitated calcium carbonate, and thensub- Jecting the latter to a pulverizing action.

4. A method of making a calcium carbonate coating pigment for paper andthe like consisting in the steps of precipitating calcium carbonate fromreacting solutions of sodium carbonate, sodium bicarbonate, and calciumchloride, in which the relative concentration of sodium carbonate tosodium bicarbonate is in the range of 2 -3 to 1, in the presence of anexcess of caicium'chloride, and agitating and heating such reactingsolutions during precipitation in a temperature range of 150 to 220 1".

HOWARD RODERICK.

